Oral Presentation 6th Australian Health and Medical Research Congress 2012

Vitamin D and Immunity (#106)

Department of Orthopaedic Surgery, The David Geffen School of Medicine at the University of California Los Angeles, Los Angeles, CA, USA

Vitamin D plays a pivotal role in calcium
homeostasis and bone metabolism.
However, studies over the last 25 years suggest that the biological
impact of vitamin D extends far beyond the skeleton to include potent
anticancer, antihypertensive and immunomodulatory effects. The latter are particularly interesting given
the historical link between vitamin D and infectious diseases such as
tuberculosis and leprosy. More recent
studies have shown that vitamin D can influence key mechanisms associated with
both the innate and adaptive arms of the immune system. Many cells within the within the classical
immune system, as well as associated non-classical immune targets such as
epithelial and stromal cells express the nuclear vitamin D receptor (VDR) that
binds the active form of vitamin D, 1,25-dihydroxyvitamin D (1,25D). In addition, antigen presenting cells such as
macrophages and dendritic cells (DCs) are capable of synthesizing 1,25D from
precursor 25-hydroxyvitamin D (25D) by expressing the activating enzyme 1α-hydroxylase (CYP27B1).
Synthesis of 1,25D by macrophages or DCs may support endogenous
intracrine responses (notably the induction of antibacterial proteins in
macrophages), but may also involve paracrine actions (notably phenotype effects
on VDR-expressing T-cells). Crucially,
all of these effects are highly dependent on the availability of the substrate
for CYP27B1, 25D, which is also the main marker of vitamin D status in any
given individual. Based on this it has
been proposed that vitamin D-deficiency may have profound effects on infection
and immunity. The aim of this
presentation will be to explore this link between the vitamin D and the immune
system in greater detail, with specific emphasis on novel immunomodulatory
mechanisms, disease-specific corruption of vitamin D responses and the scope
for clinical intervention through vitamin D supplementation.